1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt at least one of a) incorporating a load carrying member and b) having driving teeth thereon.
2. Background Art
The deterioration of rubber in an ozone atmosphere has been a problem in the power transmission belt area. Conventional belts made from natural rubber, styrene-butadiene rubber, chloroprene rubber, etc. are prone to cracking prematurely due to the deterioration of the rubber in these belts. Additionally, rubber compositions containing halogen, such as chloroprene, cause the generation of dioxin, which is undesirable from an environmental standpoint. Accordingly, the industry-has looked towards making power transmission belts from rubber that does not contain halogen.
In response to this demand, ethylene α-olefin rubbers, such as an ethylene-propylene rubber (EPR) and ethylene-propylene-diene copolymer rubber (EPDM), have been considered recently to be viable alternatives to halogen-containing rubber. These compositions are desirable from the standpoint that they have good resistance to ozone and both heat and cold. Additionally, these polymers are relatively inexpensive. The use of these compositions is disclosed, for example, in JP-A-06/345,948 (Japanese Gazette).
However, adhesive properties of an ethylene α-olefin rubber, such as ethylene-propylene rubber, are not good. Consequently, there is a problem in terms of adhering this composition to fibrous materials, such as those in load carrying members.
In addition to less than desirable adhesive properties, these rubber compositions tend to exhibit a low tearing force, which tearing force is further lowered when a peroxide cross-linking agent is used. Problems that evidence themselves are popping of the load carrying member out of the belt, as the belt is run, and breakage of teeth with a toothed belt construction. The above problems may be alleviated to a certain extent by the use of a sulphur cross-linking agent. However, when a sulphur cross-linking agent is used, it is difficult to raise the degree of vulcanization to the extent desired. This may result in increase in abrasion on the belt in use. The use of EPDM, which has many double bonds in its molecules, while increasing the extent of vulcanization and thereby increasing the resistance to adhesive abrasion to a certain extent, tends to lower heat resistance for the rubber.